The present invention relates to a liquid crystal display device, and, more particularly, to a technique which is applicable to drive circuits of a liquid crystal display device of the type used in a portable display device.
Liquid crystal display devices of the STN (Super Twisted Nematic) type or liquid crystal display devices of the TFT (Thin Film Transistor) type have been popularly used as display devices in notebook type personal computers or the like. The typical liquid crystal display device includes a liquid crystal display panel and drive circuits for driving the liquid crystal display panel.
Here, among these liquid crystal display devices, the use of liquid crystal display devices as display devices in portable terminal devices, such as mobile telephones or the like, is increasing in number. To adapt a liquid crystal display device for use as the display device in a portable terminal devices, there is a need for a further reduction of the cost, miniaturization, an enhancement of the image quality and enhancement of the reduction of power consumption, compared to conventional liquid crystal display devices. Further, when a liquid crystal display device is used as the display device in a mobile telephone or the like, a type of portable telephone set which mounts two liquid crystal display panels on one mobile telephone has been commercially available.
In display devices of the type used in portable terminal devices, such as mobile telephones, along with the spread of electronic mail to which images are attached, a further enhancement of the image display functions is demanded. Further, even when two liquid crystal display panels are mounted on one mobile telephone, both of these liquid crystal display panels are required to provide high image display functions, such as a high display quality and high definition. Still further, in view of the nature of these display devices, in that they are used as portable terminals, lower power consumption is also demanded. In addition, it is also a crucial task of the display devices which are used as portable terminals to strengthen the competitiveness in relation to cost.
As a problem which arises along with miniaturization of the portable terminal device, there is a decrease in the space for mounting drive circuits of the liquid crystal display device. Further, with respect to a method for mounting the drive circuits, there has been a demand for so-called screen centering, that is, a method in which the center line of the device and the center of a display screen are superposed on each other. This screen centering restricts the positions where drive circuits can be mounted, and, hence, it is necessary to pay sufficient consideration to the arrangement of the display devices. Further, in the conventional liquid crystal display device, although the drive circuits have been arranged at two neighboring sides of the display screen, there is a demand for mounting the drive circuits only at one side, that is, so-called three-side-free mounting. Further, it is also necessary to decrease the number of mounting parts for decreasing the mounting areas as well as for lowering the manufacturing cost.
Particularly, when two liquid crystal display panels are mounted on one mobile telephone, it is necessary to mount the drive circuits and various parts in relation to the respective liquid crystal display panels; and, hence, there arises a drawback in that the mounting area for these drive circuits and various parts is increased.
Still further, with respect to equipment, such as a mobile telephone, which is intended for use by unspecified individuals, stable operation is requested even when a manner of operation different from the usual manner of operation is performed. Accordingly, even in an unpredictable state, such as a case in which a battery which constitutes a power source of the mobile telephone slips off, an operation which is similar to the operation performed when the power source is normally turned off, which does not display the image retention on a screen, is requested.
The present invention has been made to overcome the above-mentioned drawbacks, and it is an object of the present invention to provide a technique by which one can realize an optimum drive circuit when two liquid crystal display panels are mounted in equipment using small-sized liquid crystal display devices.
The above-mentioned and other objects and novel features of the present invention will become apparent from the description provided in this specification and the attached drawings.